Sam Kerr was staring down the football pitch with her heart pounding and her knee aching as her strength and conditioning coach Aaron Holt prayed 'please don't injure yourself, Sam'. But she gritted her teeth, finished her final shuttle run, immediately caught a flight and became an international superstar. That was the last time Holt ever heard from Kerr. Until now. The Matildas captain penned a touching two-page letter to her former coach, thanking him for saving her career four years ago. "It really affected me that someone who I hold in such high regard can think of me four years later and say thanks," Holt said. "It's crazy. There's so many coaches, family and friends in her life but she had the presence of mind to say 'I wouldn't be here without that guy'. With all the accolades that she's won, it's incredible. "I wondered whether she remembered who I am. This is the whole amazing thing, she never got to thank me because after our last session she jogged back to catch a cab to the airport." Kerr was a shy 21-year-old on crutches when she came limping into Holt's office at the Australian Institute of Sport. He was given six weeks to rehabilitate a serious knee injury which left her unable to walk. If she wasn't running by the time period was up, Football Federation Australia weren't going to select the star striker for the 2015 World Cup. There were training sessions when he thought he was going to break her. There were times when he thought it was too much for her body. But Kerr never said stop. She never complained. Holt couldn't believe when she arrived 10 minutes early to each training session, already stretching and eager to go. "She was just Sam Kerr back then," Holt said. "She was just a 21-year-old kid coming in here but there was a determination in her that was pretty remarkable. "There wasn't a training session when she didn't improve and some of them were pretty nasty. It was just unbelievable. "But that's why she's one of the best players in the world, because of her attitude and work ethic. Now, four years later, she's one of the biggest international stars and the Matildas' captain. Completely changed." Kerr has since become the face of Australian football with 78 international caps, earned the NWSL Golden Boot twice and was shortlisted for the inaugural women's Ballon d'Or. The 25-year-old scored her first ever World Cup goal last week and Holt can't help but remember the frail girl whose dream hung by a thread. "She was in such a rough patch in her life," Holt said. "It was daunting because she had a dream of going to this competition but she couldn't walk. "She's come back like a big eagle saying 'look at me now'. That's what it feels like. "She came in and couldn't walk but four years later she's flying." Kerr will lead Australia in their final World Cup group fixture when they clash with Jamaica at the Stade des Alpes on Wednesday. The Matildas need a comfortable win over the Raggae Girlz to avoid meeting hosts France in the round-of-16. Holt believes the Matildas can salvage their World Cup campaign after a shaky start to the competition. "They're a very resilient group," Holt said. "Most of them have had a lot of setbacks in their life and career but they've all bounced back. It's a credit to them all, they're very strong characters." FIFA WOMEN'S WORLD CUP Australia v Jamaica: Wednesday, 5am at Stade des Alpes, Grenoble. TV: Live on SBS, SBS On Demand and Optus Sport.